I *think* I know the differences between the various snapshots for
Debian stretch but it would be nice to have my understanding confirmed
(and also some idea of their sizes).
So 'console' is a wholly non-GUI installation probably mostly intended
for a headless BBB which one is going to access via ssh.
'lxqt' is a full GUI build with graphical login and a GUI desktop.
'iot' is somewhere in between and it's this one I'm least clear about,
what does 'iot' stand for and what does it have that 'console' doesn't
(and/or what does it lack that 'lxqt' has)?
There don't seem to be 2Gb and 4Gb images for Debian Stretch so I
guess that this means the GUI version(s) can't be fitted into 2Gb any
more, is this right? How big (approximately) are they when installed?
A 'console' installation still seems pretty small, I've just
(finally!) got one installed on a 2Gb BBB and it's only using 20% of
the 2Gb so that leaves me loads of space for the sort of things I want
to do.
Chris:
Pretty much right on.
The lxqt, full GUI, full set of programming languages, etc. are typically in the range of 3.5 to 4 GB when loaded.
So not a lot of room left for a big project in the eMMC.
IoT stands for “Internet of things” and has everything but the GUI interfaces loaded.
Typically about 2 GB when loaded
Intended for network connected, but no local GUI.
Things like Python, Javascript, are loaded and ready to go.
Lots of room for most project applications.
Console is about 1 GB loaded. Minimum functional Linux installation, with full network interfaces, no GUI.
If you want to do anything, such as to run Python, you have to load it and its dependencies yourself.
But adding what you need with apt-get is usually easier than stripping out a bunch of stuff from the IoT.
The best starting point for a dedicated, custom installation and application.
— Graham
I see, thanks for the explanation of iot. So 'console' won't even
have Python? However, as you say, using apt-get to install stuff on a
console based system will certainly be easier to get to a minimal
system for a specific set of needs.
I probably only need console + python + a couple of python modules.
The console will not have Python installed. But apt-get can install Python2 or Python3 or both and all dependencies, and a minimum set of Python modules. Other modules are available with pip.
example:
sudo apt install git build-essential tree htop i2c-tools python3 python3-pip python3-smbus
— Graham
Yes, yes, OK, I know! 
I've already done 'apt install python3' and anything else needed will
surely tell me what's missing.
Thanks